Axisymmetry
Axisymmetry is symmetry under rotation over the toroidal (i.e., cylindrical) angle φ over an arbitrary value.
Axisymmetry is the basic assumption underlying the Grad-Shafranov Equation for the calculation of tokamak equilibria. In actual magnetic confinement devices, this symmetry can only apply in an approximate fashion due to the fact that the external field coils are always discrete.